GPL Question

Hey everyone,
I am currently creating my first custom WordPress theme and would like to submit it to the themes directory on wordpress.org. One of the requirements is to make sure everything complies with the GPL. I think I have a good idea of the gpl, but I want to confirm it. The theme is built with nivo slider, which has a gpl and MIT license. I wrote the CSS, and I am using WordPress functions available from the codex. For it to comply with the gpl, everyone that downloads the theme has the freedom to edit or redistribute the theme which I think they do. Is there anything I need to include with my theme? Can anyone shed some light on this?